The present invention concerns a weighing apparatus of the through-flow type, typically with a dynamic weighing system with a weighing belt introduced between an in-coming and an out-going conveyor belt.
Such an apparatus is used in various connections, e.g. for single weighing or batch weighing, where individual items are fed with mutual distance between them, so that the weight of these items, which are shorter than the weighing belt, can be determined for subsequent distribution to selected receiving stations arranged along and at the side of the out-going conveyor belt. With so-called graders, this is effected in a computer-controlled manner, in that the object here is to build up portions with pre-determined weight in the receiving stations. For this purpose, quite advanced control algorithms based on probability calculations have been developed for the batching of the items with high efficiency. It is precisely when the items pass the weighing belt individually that a weight determination with good accuracy can be achieved, so that also the total weight of a number of batched items can display good weighing accuracy.
It shall be mentioned that apparatus is also known for through-flow weighing of an irregular or even tight item flow, which can be transported further direct to summation-weighed batches in successively arranged collection containers, whereby no demands are made regarding the carrying out of a separation before the batching of the items in the individual batch containers, neither of the weighed part-portions in combination weight nor items conveyed to the grader""s dynamic weighing system. Such a summation weighing is called xe2x80x9cflow weighingxe2x80x9d, and it can be effected by means of a dynamic weighing system which, from the point of view of mechanics, can be of quite the same type as the grader""s weighing units, i.e. a simple weighing belt which can determine the weight load on a belt of a given length. With flow-weighing, a summation is determined of the load on this belt length in close correlation with the speed at which the belt is driven, while with xe2x80x9cgrader weighingxe2x80x9dxe2x80x9d the weight of the isolated item is determined, i.e. of the item which is currently lying on this belt length, and regardless of the speed of the belt, but consequently with demands concerning item separation, so that only a single item at a time can appear along the whole length of the weighing belt, possibly a number of items grouped closely together, which shall thus merely have the necessary distance from and to the neighbouring items orxe2x80x94the item groups in the item flow and of the necessarily small extent to be able to give the illusion of a single item in this flow. In both cases, the weighing equipment itself can consist of a weighing cell which constantly provides an expression for the loading on the weighing belt, but in both cases the signals arising from the weighing must be processed very differently, e.g. because with the flow measurement regard must already be paid to the speed of the belt. In principle, this is no importance for the weighing of separate individual items, but on the other hand rather for the extent of the required separation.
The invention is based on the observation that with many deliveries of items in a flow, for example when introduced from a truck to a delivery belt in a weighing plant, there arises such an uneven item distribution that this involves constant sequences with a character of respectively continuous item flow and mutually separated items or closely arranged item groups. In accordance with the known technique, care must hereby be taken that the item flow is either or preferably evened out to a uniform flow of which the weight can be determined in accordance with the flow principle, or on the other hand divided into distinct, mutually separated item units for individual weighing in accordance with the xe2x80x9cgrader principlexe2x80x9d. The question of whether the one or the other should be implemented will thus depend on whether the supply of items shall be effected for flow weighing or for grader weighing.
With the invention it has been realised that it is possible to carry out a kind of integration of these techniques based precisely on the fact that the mechanical weighing equipment can be the same for them both. Whether the equipment shall thus serve as a flow weighing system or item weighing system will solely be a question concerning a replacement between respective units for the processing of the weighing signals. Since it is desired to work with item portioning, the apparatus equipment must naturally be arranged for this purpose, i.e. with the necessary means of separation, but it is already quite common for weighing plants also to have a simple discharge end for the delivery of items which have not been selected for any of the collection containers, so that these plants will be directly suitable also for the delivery of a flow of item which have been flow-weighed, merely when this has been made possible by expedient adaptation of the weighing algorithms which are used.
Consequently, a grader can also hereby be chosen to serve either as a grader or for flow weighing, but moreover with the possibility that this choice can be made in a current or dynamic manner, i.e. in the case discussed where an arriving flow of items changes in an irregular, or for that matter regular fashion, between being a full flow and a flow of separated individual items. This can be detected using simple means, e.g. by use of fixed photo-cells, insofar that just before the arrival at the weighing belt, items or item groups appear which have both a suitably short length and a suitably short distance from the last preceding item and the next subsequent item, so that the weighing unit can accept to weigh this item or this group as a single item, which can then be handled in the grader system, while items or item groups which do not fulfil the said conditions are conveyed further for flow-weighing and for collection at the discharge end of the grader. During periods or sequences with flow-weighing it will be possible to increase the belt velocity.
The actual detection of the item distribution need not take place immediately before the feeding of the items to the weighing belt, in that with its knowledge of the belt speed the control computer will know when the scanned area will reach forward to the weighing belt. As mentioned, the scanning can be effected with means other than a photocell, e.g. a vision camera or a preceding, short weighing belt. It will also be a possibility for use to be made of the operative weighing cell itself for the scanning, in that e.g. via this it can be detected whether an arriving load has the character of a small article, which after entry on the weighing belt does not give rise to further weight increase on the belt, or whether it is a long article which when departing from the weighing belt at its leading end has not yet manifested itself by a stabilising of the weight loading of the belt.
Within the weighing technique there is a tendency for the hitherto quite clear concepts such as xe2x80x9csingle weighingxe2x80x9d and xe2x80x9cflow weighingxe2x80x9d to become less clear, in that what is involved is rather the use of algorithms which are optimised for the task which is to be solved. Therefore, in a slightly broader sense the invention is to be understood in that way that under varying conditions, a determination is made of which type of task is currently relevant, and an associated selection of which of several pre-programmed algorithms are to be preferred in the solving of the task detected.
It must be mentioned that in any case there will be a theoretical possibility for the determination of the type of task to be effected by the passage of the weighing belt itself, in that the associated signals from the weighing cell can be subjected to very quick signal analysis, and moreover stored until it is decided by this analysis which algorithm will be most suitable for the purpose. Thereafter, the stored signal sequence can be retrieved for processing by the selected algorithm, and there will hereby even be the possibility of a certain integration of the signal processing. Since this can be carried with electronic speed, the related delay in the,arrival of the weighing result will be quite modest, so that a given item in such a case can already be led out to the first of the grader""s receiving stations.
Purely from the apparatus point of view, the grader can be supplemented with equipment for the automatic changing of the receiving container for flow-weighed portions.
It must be mentioned that from the plant and capacity point of view, the invention offers the advantage that a given handling line can be better arranged for the handling of the most commonly-appearing sizes of the articles, e.g. fish, and still however also allow the passage and weighing of xe2x80x9coverlongxe2x80x9d articles which appear now and then, with the view to either the formation of portions or xe2x80x9cflow collectionxe2x80x9d. This makes it possible for use to be made of a weighing belt of quite modest length.
It will thus be a possibility for both or a number of weighing algorithms to be brought into use when the circumstances call for it, regardless of whether it is a batch weighing or a flow weighing which is given the highest priority.